The present invention relates to an electrostatic charge-removing device adapted to remove electrostatic charges formed on a light-sensitive member, specifically, in an electrophotographic copying machine or electronic printer. More particularly, the present invention is concerned with an electrostatic charge-removing device which employs a tungsten lamp as an erasing lamp.
In a conventional copying machine, such as an electrophotographic copying machine, a light-sensitive member, which is made of a material such as zinc oxide or selenium and shaped in the form of a drum, is charged positively or negatively by the use of a corona charging unit and then exposed to form an electrostatic latent image. The electrostatic latent image is developed by the use of a developing unit using toner particles having the opposite polarity to that of the electrostatic charge on the light-sensitive member. The toner image thus formed is transferred electrostatically to a recording material such as paper by the use of the corona charging unit, and the transferred toner image is fixed to produce a copied document. However, since the toner particles have the opposite polarity to that of the electrostatic charge on the light-sensitive member, they tend to adhere firmly to the light-sensitive member due to electrostatic attraction. Thus the toner image is difficult to transfer to a recording material with a high transfer efficiency. This gives rise to various disadvantages. For example, the image density of the copied image may be low. Also, since it is necessary to remove substantially all toner particles remaining on the light-sensitive member, the surface of the light-sensitive member can be scratched.
In order to overcome the foregoing problems, a procedure such as the following has been employed. As illustrated in FIG. 1, an electrostatic charge-removing device 3 is mounted between a developing unit 1 and a corona charging unit 2 for effecting electrostatic transfer. By removing electrostatic charge on a light-sensitive member 4 by the use of the electrostatic charge-removing device 3 prior to electrostatic transfer of the toner image to the recording material, the electrostatic bonding between the light-sensitive member 4 and the toner particles is released. An erasing lamp, such as a fluorescent lamp, a tungsten lamp, or the like, can be used for the electrostatic charge-removing device. In FIG. 1, reference numerals 12 and 13 indicate, respectively, a paper feeding unit and a corona charging unit for charging the light-sensitive member.
A fluorescent lamp, however, requires a stabilizer and a starter. This arrangement thus has a disadvantage in that the size of the electrostatic charge-removing device is large. Moreover, the use of a fluorescent lamp suffers from disadvantages in that a circuit must be provided to cause the lamp to light instantaneously, the amount of light output varies relatively greatly with changes in ambient temperature, and the service life is short. These disadvantages involved in using a fluorescent lamp can be eliminated by employing a tungsten lamp. In the case of a tungsten lamp, however, the peak of the spectral energy distribution lies in the infrared region. Hence, the use of a tungsten lamp is accompanied by problems such as an increase in the residual potential of the light-sensitive member and a reduction in the sensitivity of the light-sensitive member.